NAVEDTRA 15009B ACTUAL EXAM
2026/2027: 100% Verified Questions &
Correct Answers
Question 1:
A naval PWR operates at 250 MWt with an inlet temperature of 555 °F and an outlet temperature
of 595 °F. Using a primary-loop specific heat of 1.25 Btu/lbm-°F, what is the approximate total
primary coolant mass flow rate?
A. 25 × 10⁶ lbm/hr
B. 50 × 10⁶ lbm/hr
C. 62 × 10⁶ lbm/hr
D. 75 × 10⁶ lbm/hr
Correct Answer: B
Rationale: Q = ṁ c ΔT → ṁ = 250 MWt × 3.412×10⁶ Btu/hr/MWt / (1.25 Btu/lbm-°F × 40 °F) ≈ 50
× 10⁶ lbm/hr.
,Question 2:
In the S6G reactor plant, the average moderator density coefficient is –1.2 pcm/°F. A 5 °F upward
shift in average moderator temperature will produce a reactivity change of:
A. –6.0 pcm
B. –1.2 pcm
C. +6.0 pcm
D. +1.2 pcm
Correct Answer: A
Rationale: Δρ = (–1.2 pcm/°F) × 5 °F = –6.0 pcm (negative reactivity insertion).
Question 3:
The delayed-neutron fraction (β_eff) for a U-235-fueled naval reactor is ~0.0065. What is the
approximate prompt-neutron lifetime (l) that yields a reactor period (T) of +50 s at a positive
reactivity insertion of +0.5 $?
A. 5 × 10⁻⁵ s
B. 1 × 10⁻⁴ s
C. 2 × 10⁻⁴ s
,D. 5 × 10⁻⁴ s
Correct Answer: B
Rationale: Using the in-hour equation for small ρ ≈ 0.5 $, β_eff/Λ ≈ 0.0065/Λ = 1/T → Λ ≈ l ≈
1×10⁻⁴ s.
Question 4:
A main coolant pump (MCP) trip reduces loop flow by 50 % instantaneously. Assuming no reactor
scram, the immediate effect on DNBR (Departure from Nucleate Boiling Ratio) is:
A. DNBR increases due to higher exit quality.
B. DNBR decreases due to reduced heat-transfer coefficient.
C. DNBR remains constant because power is unchanged.
D. DNBR increases due to lower fuel temperature.
Correct Answer: B
Rationale: Lower mass flow reduces velocity and h, increasing clad temperature and decreasing
DNBR.
Question 5:
, Per EOSS, the maximum allowable rate of change of reactor coolant temperature during a startup
is 5 °F per 15 minutes. This limit protects against:
A. Fuel-clad mechanical interaction
B. Excessive pressurizer level swell
C. Control-rod drive housing differential expansion
D. Steam-generator U-tube over-pressurization
Correct Answer: A
Rationale: Limiting ΔT/Δt minimizes pellet-clad differential expansion and PCMI.
Question 6:
The S6G plant uses hafnium control rods. The macroscopic absorption cross-section (Σ_a) of
hafnium at 0.0253 eV is ~0.45 cm⁻¹. The thermal-neutron diffusion length L is closest to:
A. 0.5 cm
B. 1.0 cm
C. 1.5 cm
D. 2.0 cm
Correct Answer: C
2026/2027: 100% Verified Questions &
Correct Answers
Question 1:
A naval PWR operates at 250 MWt with an inlet temperature of 555 °F and an outlet temperature
of 595 °F. Using a primary-loop specific heat of 1.25 Btu/lbm-°F, what is the approximate total
primary coolant mass flow rate?
A. 25 × 10⁶ lbm/hr
B. 50 × 10⁶ lbm/hr
C. 62 × 10⁶ lbm/hr
D. 75 × 10⁶ lbm/hr
Correct Answer: B
Rationale: Q = ṁ c ΔT → ṁ = 250 MWt × 3.412×10⁶ Btu/hr/MWt / (1.25 Btu/lbm-°F × 40 °F) ≈ 50
× 10⁶ lbm/hr.
,Question 2:
In the S6G reactor plant, the average moderator density coefficient is –1.2 pcm/°F. A 5 °F upward
shift in average moderator temperature will produce a reactivity change of:
A. –6.0 pcm
B. –1.2 pcm
C. +6.0 pcm
D. +1.2 pcm
Correct Answer: A
Rationale: Δρ = (–1.2 pcm/°F) × 5 °F = –6.0 pcm (negative reactivity insertion).
Question 3:
The delayed-neutron fraction (β_eff) for a U-235-fueled naval reactor is ~0.0065. What is the
approximate prompt-neutron lifetime (l) that yields a reactor period (T) of +50 s at a positive
reactivity insertion of +0.5 $?
A. 5 × 10⁻⁵ s
B. 1 × 10⁻⁴ s
C. 2 × 10⁻⁴ s
,D. 5 × 10⁻⁴ s
Correct Answer: B
Rationale: Using the in-hour equation for small ρ ≈ 0.5 $, β_eff/Λ ≈ 0.0065/Λ = 1/T → Λ ≈ l ≈
1×10⁻⁴ s.
Question 4:
A main coolant pump (MCP) trip reduces loop flow by 50 % instantaneously. Assuming no reactor
scram, the immediate effect on DNBR (Departure from Nucleate Boiling Ratio) is:
A. DNBR increases due to higher exit quality.
B. DNBR decreases due to reduced heat-transfer coefficient.
C. DNBR remains constant because power is unchanged.
D. DNBR increases due to lower fuel temperature.
Correct Answer: B
Rationale: Lower mass flow reduces velocity and h, increasing clad temperature and decreasing
DNBR.
Question 5:
, Per EOSS, the maximum allowable rate of change of reactor coolant temperature during a startup
is 5 °F per 15 minutes. This limit protects against:
A. Fuel-clad mechanical interaction
B. Excessive pressurizer level swell
C. Control-rod drive housing differential expansion
D. Steam-generator U-tube over-pressurization
Correct Answer: A
Rationale: Limiting ΔT/Δt minimizes pellet-clad differential expansion and PCMI.
Question 6:
The S6G plant uses hafnium control rods. The macroscopic absorption cross-section (Σ_a) of
hafnium at 0.0253 eV is ~0.45 cm⁻¹. The thermal-neutron diffusion length L is closest to:
A. 0.5 cm
B. 1.0 cm
C. 1.5 cm
D. 2.0 cm
Correct Answer: C
